1. Field of the Invention
The present invention relates to an automatic density control device for controlling the density of a copied image in a copying machine.
2. Description of the Prior Art
Automatic density control devices of different types are known for use in copying machines. In one type, the density of a document to be copied is read by a scanner to determine the density of a copy image before the document is actually duplicated. According to another principle, the density of a document is read while it is being copied to determine the density of a copy image.
With the former automatic density control device, the document density is read by the scanner after the document has been set in place, and a copying cycle is started after the copy image density has been determined. Since various steps are involved to determine the copy image density before the copying cycle is initiated, the rate of overall operation of the copying machine is relatively low especially where an automatic document feeder is employed to feed documents. The latter automatic density control device determines the copy image density by reading the document density during the copying operation. Therefore, the copy image density cannot be controlled by controlling the amount of light applied to the document, and the automatic density control device is relatively costly.